Ways to calculate similarity

Question

I am doing a community website that requires me to calculate the similarity between any two users. Each user is described with the following attributes:

age, skin ty

Answer 1

Give each attribute an appropriate weight, and add the differences between values.

enum SkinType
    Dry, Medium, Oily

enum HairLength
    Bald, Short, Medium, Long

UserDifference(user1, user2)
    total := 0
    total += abs(user1.Age - user2.Age) * 0.1
    total += abs((int)user1.Skin - (int)user2.Skin) * 0.5
    total += abs((int)user1.Hair - (int)user2.Hair) * 0.8
    # etc...
    return total

If you really need similarity instead of difference, use 1 / UserDifference(a, b)